Refrigeration systems/units are frequently used in connection with the transport of goods, such as perishable food products. The mobile nature of the transport frequently presents challenges, as power sources are limited. For example, an engine that may be used to power the refrigeration unit is of a finite size, or in other words, the engine has a finite capacity.
The evolution of transport refrigeration units, at least with respect to capacity and efficiency, frequently require the system to utilize 100% of available power. When a refrigeration unit includes a multi stage compression cycle, this can lead to difficult and unstable power management. For example, in a transport system using a small engine (e.g., an engine of a relatively small capacity), there might not be an available engine power reserve between the refrigeration unit and the engine. In this regard, if a higher stage of the multi stage compression cycle is too aggressively engaged, the engine could be subjected to a high probability of stalling. On the other hand, if a higher stage of the multi stage compression cycle is passively engaged (e.g., the higher stage is engaged later than it otherwise could have been), this may result in an under-utilization of the available engine power by the refrigeration unit.
In traditional systems, an added power demand of a higher stage or economized cycle may cause a suction throttling event in response to power overload. Suction throttling for midstage injection flow is inefficient and troublesome.